Hamish Watson explains that Windows authentication is not available with Azure Managed Instances:
Azure SQL Managed Instances do not utilise windows authentication – so your two methods of authenticating applications and users are:
– SQL Authentication:This authentication method uses a username and password.
– Azure Active Directory Authentication:This authentication method uses identities managed by Azure Active Directory and is supported for managed and integrated domains. Use Active Directory authentication (integrated security) whenever possible.
Hamish also elaborates on some of the trickier bits about Azure Active Directory for someone used to on-prem AD solutions.